112 THE PRINCIPLES OF MYODYNAMICS. 



may be grouped, according- to their function, as 

 follows : — 



(i.) The extensors of the leg are the muscles 

 of the quadriceps extensor. 



(2.) The flexors of the leg are the semi-tendin- 

 osus, the semi-membranosus, the biceps cruris, 

 the popliteus, the gracilis, the sartorius, and the 

 gastrocnemius. 



(3.) The out-rotators of the leg are the biceps 

 cruris and the sartorius. 



(4.) The in-rotators of the leg are the semi- 

 tendinosus, the semi-membranosus, the popli- 

 teus, the gracilis, and the sartorius. 



105. (i.) The rectus femoris, the sartorius, 

 the semi-tendinosus, the semi-membranosus, the 

 gracilis, and part of the biceps cruris span both 

 the knee-joint and the hip-joint. 



(2.) The vastus internus, the vastus externus, 

 the popliteus, and part of the biceps cruris span 

 the knee-joint. 



(3.) The gastrocnemius spans both the knee- 

 joint and the ankle-joint. 



106. The muscles that span the knee-joint 

 may make the femur the fixed bone and the 



